DESCRIPTION (Applicant's Description): Transforming growth factor-beta1 (TGF-beta) is a growth factor with a variety of biological activities governing cell growth, production of extracellular matrix, development, and differentiation. Defects in TGF-beta signal transduction are implicated in a variety of diseases such as cancer and diabetic glomerulosclerosis. A fundamental effect of TGF-beta on cells is to regulate transcription of a broad range of genes. However, currently little is known about how TGF-beta regulates expression of a diverse range of genes and how it induces inhibition of cell growth. The applicant seeks to identify novel molecules in TGF-beta signaling pathway which activate the TGF-beta-induced gene transcription. This is made possible by taking advantage of an engineered TGF-beta responsive cell line and high-titer retroviral cDNA libraries. Novel molecules that inhibit TGF-beta signaling will also be identified using this system. The applicant will investigate how the uncovered novel molecules participate in TGF-beta signaling. Furthermore, to investigate the physiological role of a TGF-beta activated transcription factor, TFE3, this transcription factor will be knocked out in mice by homologous gene-targeting. Alternatively, transgenic mice expressing an inducible dominant negative TFE3 will be generated. Finally, an antisense RNA approach in concert with a specially designed retroviral cDNA library will be employed to isolate cDNAs encoding proteins that are essential for TGF-beta-induced growth inhibition. The novel cDNAs isolated by the antisense approach will be tested for its potential role as tumor suppressor genes.